[Proj] Question about authorship
gerald.evenden at verizon.net
Sat Mar 5 00:08:15 EST 2005
Excellent recounting of the EPSG material and certainly explains why I
much trouble with it.
My preferred approach to securing information on various grid systems
search out information form the governmental bodies involved. The Swiss
material is an excellent example where summary of projections and grid
systems is available in government pamphlets. I recently obtained
excellent material from New Brunswick where they did a very good
workup of the Double Stereographic which libproj4 emulates with
Incidentally, the Laborde material that Snyder sent me was attributed to
My main experience with EPSG is with the #7 supplement as I find the
data base too much of a pain to work with and at the time I did work
it I didn't have a suitable script to get it into MySQL or Postgress.
never built any confidence with me as I detected someone struggling
with the concepts of what was being developed. I usually get more help
from web searches. EPSG is a source of last resort.
A case I like to make are the Krovak, Swiss and Sterea projections are
easy to set up once the concept of the double projection is developed.
In libproj4 the code sections for each of these projections consists of
only a few lines of code which in turn rely upon a single routine for
conversion to/from the ellipsoid-sphere and an axis translation
Maybe the 800lb. gorilla has this approach in their system but I do not
see it elsewhere.
These projections are also demonstrative of Snyder being somewhat
parochial in his efforts as he never touched upon the general double
projection as used above in any of his material that I am aware of.
As for libproj4 being catholic: it is not but I am doing my best to
modicum of success in that direction.
Lastly, I am always appreciative of any material related to projections
VERY appreciative of bug reports.
Another release is due later this month and, at last, an expanded
On Mar 4, 2005, at 10:51 PM, Clifford J Mugnier wrote:
> The EPSG documentation is mainly authored by Mr. Roger Lott, the
> Chief Surveyor of British Petroleum Oil Company in London. Mr. Lott
> on the documentation and writings of Mr. John P. Snyder whenever Snyder
> wrote on a particular projection. However, Snyder was ONLY interested
> the map projections that were used by the U.S. Geological Survey
> (USGS) in
> his books published by the USGS. As a result, concepts germain to
> topographic mapping by the USGS were addressed by Snyder and
> by Lott.
> On the other hand, Mr. Lott was interested in world-wide useage of
> large-scale map projections used for topographic maps and navigation
> specifically with emphasis on oil exploration and production. Many of
> these were not used by the USGS and therefore Snyder did not write on
> those. As a result, the mathematical documentation by Mr. Lott on a
> lot of
> projections were a product of his own vast experience in oil
> during his world-wide career. Concepts that were promulgated by
> Snyder for
> USGS applications were not always valid for applications that Mr. Lott
> encountered during his career.
> For instance, the Hotine Rectified Skew Orthomorphic (oblique
> Mercator) is
> detailed by Mr. Lott but the Laborde Oblique Mercator is not. Why is
> It's because Mr. Lott's objective was plus or minus a tenth of a meter
> accuracy for oil exploration applications. NOT geodetic accuracy! The
> standard computer operating system for the oil patch world-wide is SUN
> Solaris (UNIX). What is the 800-pound gorilla for UNIX GIS software?
> ESRI. When the GIS Department of the Malagasy Republic (now re-named)
> needed support for their country, (Madagascar); ESRI worked up a
> set of parameters to get the Hotine RSO to produce Grid coordinates
> more or
> less compatible with the Laborde projection to an accuracy of a tenth
> of a
> meter within the land area of the island. That computational accuracy
> Mr. Lott's objective, so no further elegant mathematical
> derivation/documentation was necessary as far as the EPSG was
> Geodetically elegant? No. Practically functional as far as the "Oil
> Patch" is concerned? Yep.
> And so on and so forth for the other questions, including the
> parallel version of the Normal Mercator. It is the identical
> equivalent of the Normal Mercator with a scale factor at origin (at the
> equator) equal to a value less than unity. Why call it such? Because
> that's how NGA/NIMA (and the UK Military Survey and the UK Hydrographic
> Office) describes their charts, and that's a big deal to the "Oil
> (Same goes for the Lambert Conformal Conic).
> The EPSG mathematical documentation is excellent when you consider the
> context in which it was developed and its ultimate objectives. Same
> for Snyder's works. They both have their limitations as far as a
> treatise is considered, but I doubt that PROJ4 is a catholic treatise,
> Check out chapter three in the 5th edition of the "Manual of
> Photogrammetry" if you want some detailed math. I wrote it. There's
> a new
> "Manual of GIS" being planned by the American Society for
> and Remote Sensing, and I've been asked to write a chapter for that on
> projections also. It'll be out in a year or two; I have yet to sit
> and write the chapter.
> Clifford J. Mugnier
> Chief of Geodesy and
> Associate Director,
> CENTER FOR GEOINFORMATICS
> Department of Civil Engineering
> CEBA 3223A
> LOUISIANA STATE UNIVERSITY
> Baton Rouge, LA 70803
> Voice and Facsimile: (225) 578-8536 [Academic]
> Voice and Facsimile: (225) 578-4474 [Research]
Jerry and the low riders: Daisy Mae and Joshua.
"The whole religious complexion of the modern world is due to the
absence from Jerusalem of a lunatic asylum." Havelock Ellis, 1914
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